JACK can handle 2 buffers at most, make the default buffer allocator
allocate 2 buffers when no params are given.
Prefer 2 buffers, it allows some form of async fill/consume
This is more in line with wayland and it allows us to create new
interfaces in modules without having to add anything to the type
enum. It also removes some lookups to map type_id to readable
name in debug.
